The present invention relates to rapidly mapping and characterizing hydrocarbon and dispersant plumes in seawater.
In April 2010, the Deepwater Horizon oil drilling rig exploded, causing an oil spill at the Macondo Well in the Gulf of Mexico that was one of the largest accidental marine oil spills in the history of the petroleum industry. The well released over 200 million gallons of crude oil into the Gulf of Mexico, resulting in damage to marine and wildlife habitats and to fishing and tourism industries, as well as health concerns to inhabitants of the Gulf coastline. Although the well was eventually capped, the impact of this massive spill continues today, and will continue for years to come.
Masses of undersea oil, which have lengths spanning tens of miles, have been reported in the Gulf of Mexico. These oil or hydrocarbon plumes, plus the vast quantities of toxic chemicals (such as COREXIT oil spill dispersants by Nalco Company) intended to disperse them, move and spread in the Gulf seawater column, posing long-term threats to marine and coastal wildlife. The volatile components of the plumes floated to the surface early, where they could be burned off, but the vast majority of the oil either sank (smothering life on the seafloor) or drifted away with the Gulf Loop Current.
Such a huge and amorphous target is extremely expensive and difficult to accurately characterize. Determining the character of a hydrocarbon plume currently requires stopping a $100,000-per-day ocean-going vessel in the water for several hours, and dropping sampling bottles over the side to depths in excess of a mile. Only an extremely tiny sample of the water column is collected, which must then be analyzed later in a laboratory, adding days of additional time. The entire process operates under the implicit assumption that the oil plume does not move during the hours needed to do the sampling, which is not a valid assumption.
Other existing methods that can be used to map hydrocarbon plumes in seawater include sonic methods (e.g., side-scan sonar) and resistivity. However, sonic methods require a significant velocity contrast to function, and a dispersed hydrocarbon plume will have a sound velocity indistinguishable from unpolluted seawater, rendering this approach ineffective away from the erupting seafloor well-head. Resistivity methods will not work because the sampling current will short-circuit past the oil droplets following the path of least electrical resistance through the highly-conductive seawater, rendering this approach equally ineffective.
Besides the Macondo Well blowout, there have been a number of other major well-blowouts and oil leaks in the open ocean, including several larger than the Macondo Well event. Notable among these are the Ixtoc Well (Bay of Campeche, 1979) and the Persian Gulf (1991), which each released larger volumes of oil. At this time, there is no way to really know what remains from these huge pollution events, since divers can rarely descend below 100 meters, and people controlling remotely-operated underwater vehicles can see little more than divers in low-visibility, dark waters.
Also, there are over 6,600 active or removed oil platforms in the Gulf of Mexico alone, and each connects to a huge network of pipelines lying on or just below the seafloor. These pipelines convey oil from all the current and former offshore oil platforms and wells to collection points and refineries on land. Many of these pipelines are old, corroded, or damaged by hurricanes, and are known to be leaking. In addition, the Gulf of Mexico has many natural oil seeps.
To protect coastline and marine environments, new technologies are needed to detect, map, and characterize undersea hydrocarbon plumes, and to predict their movements.